The host–guest inclusion driven by host-stabilized charge transfer for construction of sequentially red-shifted mechanochromic system

Developing more extensive methods to understand the underlying structure-property relationship of mechanochromic luminescent molecules is demanding but remains challenging. Herein, the effect of host-guest interaction on the mechanochromic properties of organic molecules is illustrated. A series of pyridinium-functionalized triphenylamine derivatives show bathochromic-shifted emission upon mechanical stimulation. These derivatives bind to cucurbit[8]uril to form homoternary host-guest inclusion complexes through host-stabilized intermolecular charge transfer interactions. Remarkably, the homoternary complexes exhibit longer emission than that of free guests in the solid state (even longer than ground guests), and a further bathochromic-shifted emission is observed upon grinding. Additionally, a heteroternary complex constructed through the encapsulation of pyrene (donor) and pyridinium (acceptor) guest pair in cucurbit[8]uril also displays the mechanochromic luminescent property. This work not only discloses the effect of host-guest inclusion on the mechanochromic property of organic molecules, but also provides a principle and a facile way to design the sequentially red-shifted mechanochromic materials.


Supplementary Figure 1. Synthetic routes for G1-G3.
Synthesis of 1a were adapted and modified from previously reported procedures. [1] 4-Bromotriphenylamine (1.0 g, 3.08 mmol) was dissolved in 15 mL DMF, phosphorus oxychloride (0.35 mL, 3.70 mmol) was then injected to the solution. The mixture was stirred at 383 K overnight. Then the mixture was poured into 150 mL H 2 O, and the solid was collected and purified by means of column chromatography (petroleum ether/ethyl acetate 20:1) to give compound 1a as a green solid (0.77 g, 71%). 1a: 1

Synthesis of G1-PF 6 :
1b (0.50 g, 1.43 mmol) was dissolved in dry DCM (10 mL) and CH 3 I (1 mL) was injected. The mixture was stirred at room temperature for 12 h. Then acquired yellow solid and the reaction mixture was filtered, washed with DCM and dried in vacuum to give yellow solid. Then the yellow solid was dissolved in MeOH:H 2 O (1:1, 20 mL), added excess NH 4 PF 6 to the solution and the filter cake was filtered, the obtained solid was washed with H 2 O for three times in order to wash off excess NH 4 PF 6 , dried in vacuum at 60°C to give green solid (0.45 g, 86%).

Synthesis of G1-Cl:
The yellow solid G1-Cl was given in yield of 90% after thorough counter anion exchange in water using Amberlite® IRA-400(Cl) resin (by simply shaking the suspension of the G1-PF 6 and resin in water overnight) and lyophilization. G1-Cl: 1  Synthesis of 2a/2b was adapted and modified from previously reported procedures. [2] 4-Bromotriphenylamine (1.0 g, 3.08 mmol) was dissolved in 15 mL DMF, phosphorus oxychloride (2.5 mL, 26.46 mmol) was then injected to the solution. The mixture was stirred at 383 K overnight. Then the mixture was poured into 150 mL H 2 O, and the solid was collected and purified by means of column chromatography (petroleum ether/ethyl acetate 12:1) to give compound 2a as a green solid (0.88 g, 75%). 2a: 1  Synthesis of 3a/G3 was adapted and modified from previously reported procedures. [3] Potassium carbonate (1.03 g, 7.44 mmol) and tetrakis(triphenylphosphine)palladium(0) (0.21 g, 0.12 mmol) were added to a stirred solution of 4-Bromo-N-(4-bromophenyl)-N-phenylaniline (0.50 g, 1.24 mmol) and 4-pyridinylboronic acid (0.31 g, 2.48 mmol) in degassed THF (60 mL). The mixture was heated under reflux for 24 h under the protection of N 2 gas and then concentrated. The mixture was then evaporated and purified by means of column chromatography to give compound 3a as a light yellow solid (0.32 g, 65%). 3a (0.40 g, mmol) was dissolved in dry DCM (15 mL) and CH 3 I (0.6 mL) was injected. The mixture was stirred at room temperature for 24 h. Then acquired red solid and the reaction mixture was filtered, washed with DCM and dried in vacuum to give red solid. Then the solid was dissolved in MeOH:H 2 O (1:1, 30 mL), added excess NH 4 PF 6 to the solution and the filter cake was filtered, the obtained solid was washed with H 2 O for three times in order to wash off excess NH 4 PF 6 , dried in vacuum at 60°C to give yellow solid. Compound G3 was obtained (0.36 g, 72%) after thorough counter anion exchange in water using Amberlite® IRA-400(Cl) resin (by simply shaking the suspension of the yellow solid and resin in water for 20 h) and lyophilization. G3: 1  Glycoluril (100 g, 0.7 mol) and paraformaldehyde (42.2 g, 1.4 mol) were added to a two-necked flask, and then conc. HCl (75 mL) was added. The mixture was heated at 373 K for 18 h. The mixture was poured into CH 3 OH:H 2 O (6:1, 500 mL), the obtained white solid was then washed with water for 5 times (200 mL×5). The resulted white solid was dissolved in 200 mL conc. HCl, and 600 mL H 2 O was then added into the solution, the crude product of CB[8] precipitated out of the solution. CB[8] was obtained (7.0 g, 6%) by recrystallization the crude product in 9 M HCl for twice. CB

ITC data for G1 with CB[8]
Supplementary Step 2 3.758 × 10 5 -31.82 -35.31 -11.71 [a] The standard free energy (ΔG) can be obtained according to the following equation: where T is the absolute temperature.

Solid state absorption spectra of G1 and CB[8]ꞏG12
Supplementary Figure 36. Solid state absorption spectra for the as-prepared and ground samples of G1 and CB[8]ꞏG1 2 .

Host-guest recognition and MCL behavior of CB[8]ꞏPyꞏG1
Supplementary

Crystal data
Supplementary